YARN-4400. AsyncDispatcher.waitForDrained should be final. Contributed by Daniel Templeton.

(cherry picked from commit bb5df272b9)

hadoop-yarn-project/CHANGES.txt

@@ -1130,6 +1130,9 @@ Release 2.8.0 - UNRELEASED
     YARN-4477. FairScheduler: Handle condition which can result in an
     infinite loop in attemptScheduling. (Tao Jie via asuresh)
 
+    YARN-4400. AsyncDispatcher.waitForDrained should be final. (Daniel Templeton 
+    via junping_du)
+
 Release 2.7.3 - UNRELEASED
 
   INCOMPATIBLE CHANGES

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/event/AsyncDispatcher.java

@@ -59,7 +59,7 @@ public class AsyncDispatcher extends AbstractService implements Dispatcher {
   // Indicates all the remaining dispatcher's events on stop have been drained
   // and processed.
   private volatile boolean drained = true;
-  private Object waitForDrained = new Object();
+  private final Object waitForDrained = new Object();
 
   // For drainEventsOnStop enabled only, block newly coming events into the
   // queue while stopping.